Electrophotographic developing apparatus



Feb. 16, 1965 W. C. YORK ELECTROPHOTOGRAPHIC DEVELOPING APPARATUS Filed May 4, 1961 WILL/AM c. YORK INVENTOR.

WM ma.

' ATTORNEYS United States Patent amass? No. rev se The present invention relates to electrophotography and particularly to those forms which use liquid developers.

One form or" xerography has the toner particles suspended in liquid and many forms of photoconductography use liquid e ectrolytes as the developer. The present invention has to do with apparatus for applying liquid developers of either type to the surface to be toned or developed.

It is the object of the invention to apply fresh developer to the surface of an imagewise exposed photoconductive layer which is continuously moving. The developer must extend over sufficient area of the moving web to provide adequate time for development and means must be included to insure a substantially uniform electric field at the surface being developed. It is dillicult in practice to meet all of these requirements simultaneously and the object o: the present invention is not only to meet the requirements adequately but to do so in a manner which results in excellent prints.

In accordance with the invention the above objects are accomplished by the following arrangement. The exposed photoconductive sheet is moved through a flat or curved area with the surface to be developed facing more or less downward. The area could be horizontal but it is not necessarily so. The developer solution, containing suspended particles in the case of xerography developer and containing electrolyte in the case of photoconductography, is located below the area. A roller is provided which is partly immersed in the developer and rotation of the roller carries the developer up to a point or longitudinal line on the roller, at or near the top thereof, at which ine the developer contacts the surface of the photoconductive sheet. For reference purposes the developing area through which the photoconductive sheet moves, is deli. ed with reference to a substantially horizontal straight lure approximately at right angles to the direction of motion of the sheet, which line constitutes one edge of the area. The sheet may be moving in either direction so that this reference edge is the first edge reached or the last edge passed by the sheet.

The rotating roller carries the developer to this reference line and rotation of the roller drives or pumps the developer onto a metal apron so that the developer moves between the apron and the surface of the film to be developed. The apron is parallel to the development areas and is spaced therefrom between ,6 and fi of an inch. The roller may be slightly farther from the development area providing it drives the developer up onto the apron. That is, the roller is spaced from the moving sheet, specifically from the reference line a distance between 4 and 4 inch. The axis of the roller is parallel to the reference line.

The apron is normally electrically conducting, preferably of metal and through appropriate electrical connections, it constitutes one of the electrodes creating the electric field at the surface to be developed.

in the case of xerographic development, it is sometimes desirable to use insulating materials such as plastics or glass in the construction of "the roller and apron. Development then occurs preferentially at the boundaries between areas of different densities of stored charge (usually called rringe development). This is roughly equivalent "ice to the type of development obtained by immersing the surface bearing the electrostatic latent image in a large tank of developer; however, with the roller/ apron apparatus and its associated high agitation rate, more uni form and rapid development can be accomplished.

The rotation of the roller past the reference line is always toward the apron, whether the photoconduotive sheet is moving in the same direction or in the opposite direction past the reference line. When the sheet is moved in the same direction as the developer past the reference line, it tends to carry the developer into the space between the sheet and the metal apron and this permits wider latitude of spacing between the sheet and the apron and a wider latitude of roller speeds. Faster turning rollers provide greater pumping action and when this pumping action is opposed by the direction of motion of the photoconductive sheet, it is desirable to have somewhat higher speeds of rotation of the roller. Thus the embodiment in which the sheet moves in the same direction as tie developer, is often preferable.

in a preferred embodiment of the invention the apron extends from the reference line a distance between /2 inch and 10 inch while still parallel to the area through which the photoconductive sheet moves. The remote end of the apron is preferably arranged so that the developer solution is conducted back to the developer supply bath for reuse.

When the photoconductive sheet is held fiat, the apron parallel thereto is also fiat and both may be either horizontal or inclined. When the photoconductive sheet is wrapped around a drum so that the developing area is cylindrical, the apron is adjacent to the periphery of the drum and is substantially concentric therewith to maintain the constant separation of the sheet and apron which constancy of separation is necessary to insure uniformity of electric field.

The objects of the invention and the principles thereof will be more fully understood when read in connection with the accompanying drawing in which:

PEG. 1 schematically illustrates one embodiment the invention.

FIG. 2 similarly illustrates a second embodiment of the invention.

FIG. 3 is a plan view of the embodiment shown in in FIG. 1 a photoconductive layer 10 carried on a conarrangement shown in FlG. 1.

in IG. 1 a photoconductive layer 16 carried on a conducting support 11 is moved in either direction as indicated by the double headed arrow 12 through a developing area extending from the point 13 to the point 14. in FIG. 1 the point 13 is the end view of a horizontal straight line which constitutes the reference line identified in order to simplify the description of the operation of this invention. PEG. 3 shows that the development area is bound by the edges of the photoconductive sheet consisting of layers it) and 11 and by the broken lines 13 and 14 as in this FIG. 3. FIG. 1 shows a container 20 containing an electrophotographic developer 21. This developer is a suspension in the case of liquid xerography, containing toner particles in an electrically insulating liquid. In the case of photoconductography this developer 2i is an electrolyte containing a plateable ion or any of the other developing materials employed in the various forms of photoconductography. See, for example, the von Bronk British Patent No. 188,030. According to the invention a roller 22 part.y immersed in the developer 21 is rotated by a motor (indicated at 23 in FIG. 3) so that it carries developer up as shown at 24 past the reference line 13 into the developing area. According to the invention a metal apron 26 which in this case extends beyond the ecgcs of the photoconductive sheet and hence beyond the edges of the developing area is positioned parallel to and below the area. The first edge 27 of the apron 26 is located near the reference line 13. It may actually be in contact with the surface of the drum 22 to act as a do'ctorblade or it may be spaced slightly'therefrom so that'sorne of the developer 21 is carried past the lead edge 27 and back into the container 20. In every case, some of the developer is driven by the rotation of the drum 22 into the space between the apron 26 and the photoconductive layer 10. 2

The apron 26is uniformly spaced from the developing area i.e. from the surface of the moving sheet 10, a distance between igand inch. The drum in FIG. 1 is spaced this'same distance from'the line 13 but may be spaced slightly more or slightly less than the spacing of the apron 26. The remote end 28 of the apron 26 is The return system may be more elaborate than that illustrated, ,but the illustrated form is quite satisfactory. In

the arrangement shown in FIG. 1 the effective area of the:

apron 26 is flat and parallel to the flat, surface of the photoconductive sheet 10.

In FIG. 2 on the other hand a photoconductive sheet 31 is moved through two developing areas which are cylindrical in form. The sheet 31 is wrapped on and driven by a rotating drum 32. The first developing area has a reference line 33. Developer 36 in a container 37, is carried to and past this reference line'33 by a rotating drum 39 rotated by a'motor 45. According to the invention a metal apron 40 concentric with the drum 32 is located parallel to the developing area whose reference edge'is located 'at 33. The developer 36 passes from the drum past the reference line '33 into the space between the photoconduct-ive sheet 31 and the apron 4t). Rotation of the drum 39 forces fresh developer into this space and the excess drips back into the supply reservoir 36.

' Further development is provided as the film continues into a second'development area whose horizontal reference line is at 42. In this case the movement of the photoconductive sheet 31 is opposite to that of the developer 39 as his carried by a drumdll, rotated by a motor 46, past the reference line 42 and between the photoconductive sheet31 and a second apron 4-4.- In each case,

. be immersed in the same developer solution 36 as shown.

Simply by using two separate containers separated as indicated by broken line 38, the successive stages of processing may be quite different. For example developer may be'ap'plied bythe roller 39 and, from a separate container, washing or stabilizing solution can be applied by a second roller such as that shown by 43. Once again arranged so that excess developer flowing past this end is returned to the container as indicated by the drop 29.

motor 52 carries developer past the reference line 56) and over an apron 53 whose first edge E lis adjacent to the'reference line and Whose remote edge 55 is parallel thereto. The pumping action of-the roller 51 tends to move the developer transversely across the apron and sheet 11, but in practice this is not particularly newssary. It is more important to be sure that the'developer continues in contact with the surface being developed for the same length of time and at all points across the sheet. Accordingly the arrangement shown in FIG. 3 is preferable and that in FIG. 4 is merely to indicate that the orientation of the reference line at the edge of the developing area is not too critical. It is always approximately horizontal to insure uniformity of how to the developer onto the apron, but this is also not too critical. The essential point is thatthe rotation of the roller drives the developer into the space between the apron and the photoconductive sheet and this space is maintained substantially uniform across the whole developing area.

The inventionhas been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be elfected within the spirit and scope of the invention asdescribed hereinabove and as defined in the appended I claim:

1. For use in an electrophotographic developing process in which a liquid electrophotographic developer is applied to the surface of a continuously moving image wise exposed pho-toconductive sheet, the cornbinationof means for moving the imagewise exposed sheet through an area one edge of which is a horizontal straight line approximately at right angles to the direction of motion of the sheet, a roller with its axis of rotation lower than and parallel to said line and spaced therefrom a distance.

exceeding the radius of the roller by between and 4 inch, means'for applying liquid electrophotographic developer to the roller below said line, means for rotating the roller to carry developer to and past said line to develop the surface of the imagewise exposed photoconductive sheet and meansto provide a substantially unithe aprons 40 and Mare spaced a uniform distance from, the drum 32 which isalso of metal and this permits a uniform electric field to be applied between the apron and the drum so that there is a uniform electric field at the surface of the photoconductive sheet 31 which is being developed. The electrical connections are not part'of the present invention and are hence not shown. In some forms of xerography, for'example, it is merely necessary to have the apron grounded, as indicated at 25. In photoconductography on the other hand, the apron acts as one of the electrodes in anelectrolytic system.

FIG. 4 is included primarily to illustrate that the horizontal reference line identified as 50 in this case, need not be exactly at right angles to the direction of travel of the photoconductive sheet 11. FIG. 4 is somewhat form electric field at the surface being developed and including'an electrically conductive apron below and parallel to said area and spaced therefrom between and inch, the first edge of the apron being on the side of said.

line toward which the developer moves as it is carried past said line andso close to said roller and line that developeris driven between the apronland the sheet, the edge of said apron remote from said line being adapted for conducting developer away from said area, whereby. said developer fiows into said area at said first edge and "5. The combination according to claim 1 in which the 7 sheet moving means moves the sheet in the same direction as the'developer is moved by the roller past. said line.

, 4. Thecombination according to-claim 1 in which the edge of the apron remote from said line is adjacent means for conducting developer therefrom back to said developer applying means.

5. The combination according to claim 1 in which said area and said apron are flat. i

6. For use in an electrophotographic process in which a liquid developer is applied to the surface of a photoconductive sheet, the combination of a drum for moving the sheet through a cylindrical area near the periphery of the drum, one edge of said area being a horizontal straight line approximately at right angles to the direction of motion of the sheet, a roller with its axis of rotation lower than and parallel to said line and spaced therefroma-distance exceeding the radius of the roller by between M and inch, means for applying developer to the roller below said line, means for rotating the roller to carry developer to and past said line and an electrically conductive, cylindrical apron substantially concentric with said area and the drum, the apron being positioned below and parallel to said area and spaced therefrom between A,; and & inch, the first edge of the apron being on the side of said line toward Which the developer moves as it is carried past said line and so close to said roller and line that developer is driven between the apron and the sheet, the edge of said apron remote from said line being References tilted in the tile of this patent UNETED STATES PATENTS 2,253,060 Clearrnan Aug. 19, 1941 2,529,99 Lach Nov. 14, 1950 2,99l,754 Johnson July 11, 1961 3,938,073 Johnson June 5, 1962 

1. FOR USE IN AN ELECTROPHOTOGRAPHIC DEVELOPING PROCESS IN WHICH A LIQUID ELECTROPHOTGRAPHIC DEVELOPER IS APPLIED TO THE SURFACE OF A CONTINUOUSLY MOVING IMAGEWISE EXPOSED PHOTOCONDUCTIVE SHEET, THE COMBINATION OF MEANS FOR MOVING THE IMAGEWISE EXPOSED SHEET THROUGH AN AREA ONE EDGE OF WHICH IS A HORIZONTAL STRAIGHT LINE APPROXIMATELY AT RIGHT ANGLES TO THE DIRECTION OF MOTION OF THE SHEET, A ROLLER WITH ITS AXIS OF ROTATION LOWER THAN AND PARALLEL TO SAID LINE AND SPACED THREFROM A DISTANCE EXCEEDING THE RADIUS OF THE ROLLER BETWEEN 1/64 AND 1/4 INCH, MEANS FOR APPLYING LIQUID ELECTROPHOTOGRAPHIC DEVELOPER TO THE ROLLER BELOW SAID LINE, MEANS FOR ROTATING THE ROLLER TO CARRY DEVELOPER AND PAST SAID LINE TO DEVELOP THE SURFACE OF THE IMAGEWISE EXPOSED PHOTOCONDUCTIVE SHEET AND MEANS TO PROVIDE A SUBSTANITALLY UNIFORM ELECTRIC FIELD AT THE SURFACE BEING DEVELOPED AND INCLUDING AN ELECTRICALLY CONDUCTIVE APRON BELOW AND PARALLEL 